Numerical investigation of convective transport in redox flow battery tanks: Using baffles to increase utilization

The efficient transmission of redox-active electrolyte between redox flow battery (RFB) tanks and their reactors is essential to utilizing charge capacity in grid-scale installations. Emerging redox-active electrolyte chemistries with high viscosity motivate operating RFBs near stoichiometric flow conditions, challenging the utilization of charge capacity due to convective transport limitations. In this work we use numerical simulation to resolve convective transport within RFB tanks that are free-flowing or configured with baffles by solving the laminar vorticity transport equation and transient species diffusion in two dimensions. Dead zones within free-flowing tanks are found to limit capacity utilization, while baffles are shown to enhance capacity utilization by eliminating dead zones for baffles that nearly span the tank. Utilization is maximized at a particular Péclet number, which depends on the effective length and throat of the serpentine flow path produced by baffles. These effects are shown to result from competition between transverse and longitudinal diffusive transport relative to the local flow.